Deleterious Materials & Surface Coatings of Aggregates

Deleterious Materials & Surface Coatings of Aggregates

• Deleterious Materials in Aggregates:

  • Definition: Unwanted, harmful materials that negatively affect the quality and durability of aggregate materials.
  • Types of Deleterious Materials:
    • Clay and Silt: Can retain water and weaken the aggregate structure.
    • Organic Material: Includes plant matter which can decay and reduce aggregate strength.
    • Salt Contamination: Leads to efflorescence and potential long-term damage.
    • Other Contaminants: Sulfides, gypsum, and other minerals which may react chemically causing degradation.

• Surface Coatings of Aggregates:

  • Overview: Coatings refer to materials that adhere to the surface of aggregate particles.
  • Types and Effects:
    • Clay Coatings: Adhere tightly, causing difficulty in fully binding with cement, reducing concrete strength.
    • Dust and Fine Particles: Prevent proper bonding of aggregate with binding materials, resulting in weaker structures.
    • Oxide Films: Iron oxide or similar films can create a barrier to bonding, impacting the durability and cohesiveness of the final product.
  • Handling and Treatment:
    • Washing: Effective in removing dust, clay, and fines.
    • Screening: Used to separate fine particles from the desired aggregate size.
    • Chemical Treatments: Sometimes utilized to neutralize or remove harmful coatings.

• Implications for Construction:

  • Quality Control: Regular testing and treatment of aggregates to ensure contaminants are minimized.
  • Economic Impact: High-quality, clean aggregates can reduce maintenance costs and increase the lifespan of construction projects.
  • Regulatory Standards: Compliance with industry standards and guidelines for aggregate quality and allowable levels of deleterious materials.

Key Terms:

• Deleterious: Harmful or damaging.
• Aggregate: Materials such as sand, gravel, or crushed stone used in construction.
• Surface Coatings: Externally adhered materials on aggregate particles.
• Efflorescence: White, powdery deposit on surfaces due to salts.

These notes cover the primary concepts related to deleterious materials and surface coatings in aggregates, emphasizing their types, effects, and treatments applicable in construction.